Suggestions for resolving memory leaks

These changes are suggestions for resolving memory leaks
And the some buffers, which are allocated by "pocl_aligned_malloc", are
deallocated by "free". It makes some troubles. I also suggest all malloc
and calloc should be changed to "pocl_aligned_malloc" also "free" should
be changed to "pocl_aligned_free"
Same here. Remove [Suggested by leekiju], but leave the rest as the comment is useful here.